Glow lamp



Aug. 11, 1936. D KNOWLES 2,050,341

GLOW LAMP Filed 001;. 6, 1928 INVENTOR -Dewey D. Knowles Patented Aug.11, 1936 I UNITED S'l ATES GLOW LAMP Dewey D. Knowles, Wilkinsburg, Pa.,assignor to Westinghouse Electric & Manufacturing Company, a corporationof Pennsylvania Application October 6, 192s, Serial No. 310,733

12 Claims. (01. 176-122) My invention relates to glow-discharge lampsand particularly to glow-discharge lamps adapted for use in televisionand other devices where rapid variation of light intensity is necessary.

One object of my invention is to provide a light source combining highintensity, small dimensions, and ability to respond instantaneously tovariations the electric current supply thereto.

Another object of my invention is to provide a light source combininghigh intensity with small dimensions and ability to respond rapidly tovariations of current supply and having a long operative life devoid ofchanges in luminous efllciency.

Another object of my invention is to provide a light source oi. highintensity and capable of rapid response to variations of current supplyand in which the major portion of the emitted light is projected in apredetermined direction.

Another object of my invention is to provide a glow-discharge lampadapted to provide a light source of high intensity and small dimensionswhich avoids deterioration of the transparency of the walls of thecontaining vessel through cathode sputtering of the metals constitutingthe electrodes.

A further objector my invention is to provide a light source of highintensity and capable of rapid response'to variations of excitingcurrent in which the luminous'area has the form of a relatively long andnarrow line.

Other objects of my invention will be apparent upon reading thefollowing specification, in which Figure 1 is a view, partly in sectionand partly in elevation, of a glow-discharge lamp embodying .one form ofmy invention, and

Fig. 2 is a view, partly in section and partly in elevation, of anotherform of glow-discharge lamp embodying the principles of my invention.

Fig. 3 is a view, partly in section and partly in elevation, .of anotherbut, simpler, form of glowdischarge lamp embodying principles of myinvention.

For many purposes, such as television or photofilm work, a light sourceis desired which has a high intensity but which is capable of accurateand instantaneous response to rapid fluctuations of some electricalcontrolling quantity. One of the best devices of this charactercomprises an electrical-discharge tube in which a glow discharge takesplace between a pair of cold electrodes immersed in a gas at asubstantial pressure. For many such devices, it is essential that thelight source shall be concentrated into a relalight is projected isnegligible.

tively small area, but that the luminous intensity of this area shall berelatively high.

In accordance with one feature of myinvention, I provide a light sourceof the above-described character by producing an electrical dis- 5charge between two electrodes, one of whichis positioned in the interiorof a chamber of insulating material having a single opening in its wallsof the size and shape of the luminous source desired. The cooperatingelectrode is positioned outside this chamber, preferably, closelyencircling the opening aforesaid. Electrical discharge produced througha low-pressure gas between these two electrodes is concentrated in theopening aforesaid which thereby provides a luminous source of very highintensity, capable of substantially instantaneous response tofluctuations of the supply voltage.

It is a defect of many glow-discharge lamps of the prior art that theelectrical discharge causes 2 what is known as cathode sputtering; thatis to say, the surface metal of the cathode being bombarded by thepositive ions carrying current through the tube is projected on to thesurrounding walls of the container and ultimately renders them opaque tolight. The luminous efiiciency of the tube, accordingly, rapidlydeteriorates with use. In accordance with a feature of my invention,this deterioration of the transparency of the tube walls issubstantially prevented by employing an annular cathode within a hollowanode, the only opening in the wall of which, constituting the path ofthe electrical discharge, is of such small dimensions that virtually nosputtered metal finds its way thereto. Such small amounts as areprojected through this small window can scatter over a portion of wallspace outside the anode but the amount deposited on the particular spotin the wall through which usef In accordance with another embodiment ofmy invention, the anode is separated from the oathode by a tube ofinsulating material through which the luminous discharge is compelled topass; and the light emitted by this discharge is compelled to pass, inturn, through a relatively small perforation in an opaque screen, thisperforation, accordingly, acting as the luminous source of small area.The cathode is then made in the form of a ring having its center on theline connecting the insulating tube and the perforation in the screen,and of such diameter that any sputtered metal emanating from this ringand passing through the aperture in the screen cannot'lodge on thatportion. of the tube wall through which the useful light beamisprojected.

With the foregoing purposes and principles in mind, my invention may beunderstood by reference to the accompanying drawing, in Fig. 1 of whichI designates a tube. of glass or other transparent vacuum-tightmaterial. Within the tube I, and, if desired, continuous with the wallsthereof, are the walls 2 of an internal chamber enclosing an annularelectrode 3 except for an aperture I of the size and shape of thedesired luminous source. The electrode 3 may be of any suitable metalsuch as tungsten or tantalum. I have found the latter material to permitthe flow of discharge current of much greater density than is possiblewith other cold solids without substantial sputtering of metal and otherdeterioration. Covering the exterior of the chamber 3 from the edge ofthe aperture 4 to a point well behind the electrode is a sheath of metal5, such as nickel, tungsten or tantalum, which constitutes a secondelectrode. Both of the foregoing electrodes are provided with suitableinleading wires 6, I in forms well known in glass-blowing art, those tothe electrode 3 being provided with sleeves 8, 9 of insulation, forinstance, glass or quartz. The diameter of aperture 4 and of annularelectrode 3 are so related that any particle of metal projected from thelatter through the former does not impinge on the central area of thetube wall through which the light emanating from aperture 4 is projectedthrough the aperture in electrode 5.

The discharge tube so constructed is evacuated to a high degree byprocesses too well known in the vacuum-tube art to'require descriptionhere and is then filled with some gas, preferably belium, mercury vapor,or neon, at a pressure which may be substantially 1-1 of an atmosphere.The precise pressure and the gas to be employed depend upon the colorand the quality of the light desired, but the foregoing will be foundsuitable for many purposes.

By connecting the electrodes above described to a suitable source, thecurrent in which it is controlled is in accordance with any modulatingquantity, the variations of which it is desired to reproduce in a beamof light. It will be found that the aperture in the chamber 2 .acts as aluminous source of high intensity and instantaneous response of thecharacter desired.

It will likewise be found that the major portion of the light emittedfrom this source coincides, in direction, with the line connecting thecenter of the aperture 4 with the central axis of the electrode 3, andthat, correspondingly, there is produced, in efl'ect, a concentratedlight beam.

For certain purposes, it may be found desirable to give the form of theaperture 4 that of a long narrow rectangle. In such cases, a readymethod of producing such an aperture consists in forming the walls ofthe chamber 2 of a bore-silicate glass, known in the art as G'I02P,sealing a piece of molybdenum, having the dimensions of the sealdesired, into the end of the chamber where the aperture is intended tobe, pemiitting the glass to cool, and pulling the molybdenum out. Whenthis is done, a long thin slit or aperture will be left in the chamberwall.

While there are numerous ways of forming the metallic sheath 5constituting the external electrode surrounding the chamber 2, it willbe found that this may be conveniently done by coating the exterior ofthe glass with a silver mirror, or by depositing metal thereon, by theSchoop spray process. These methods are particularly applicable wherethe narrow form of aperture is produced by employing molybdenum in themanner just described.

In the embodiment of my invention shown in Fig. 2, ll designates a tubeof glass or other insulating material consisting of two bulbs connectedby a relatively narrow tubular neck l2. In one of these bulbs is sealedan electrode l3 which may be in the form of. a ring shaped plate, while,in the other bulb, is sealed a cooperating electrode in the form of aring l4. 0n the side of electrode I4 remote from the tube I2 ispositioned a screen I! which may be of metal and is provided with anorifice i6 aligned with the axes of the tube l2 and the electrode I4.The aperture I6 is made of the size and shape of the luminous sourcedesired.

A tube, constructed as indicated in Fig. 2, is evacuated and filled witha suitable atmosphere of gas. As stated in connection with Fig. 1, the

precise gas and its pressure depend somewhat upon the use to which theglow lamp is to be put, but substantially 1-1/100 of an atmosphere ofneon, mercury vapor or helium will be found suitable for many purposes.

When the electrodes I 3 and H are connected to a suitable control sourceof electric current, a glow discharge occurs between them which isconcentrated to a high intensity along the narrow tube i2. Lightemanating from this portion of the glow discharge is projected throughthe aperture l6, thence through the end wall I! of the tube and out toany desired point. It will be found that the major portion of theemitted light is concentrated in the axis connecting the tube l2 and theaperture i6 and that, accordingly, a relatively concentrated beam ofparallel rays results.

By reason of the relative positions of the aperture l6 and the peripheryof the ring electrode it, it will be seen that any particles sputteredfrom the surface of the latter by the electrical discharge and projectedthrough the aperture is will strike portions of the tube wall other thanthat traversed by the light beam. In consequence of this, thetransparency of the portion ll of the tube wall remains practicallyundeteriorate'zl throughout the life of the glow lamp.

Another yet simpler structure embodying my invention is illustrated inFig. 3 in which a vacuum-tight envelope 2| is filled with gas in thesame manner as the tubes shown in Figs. 1 and 2. A tube 22, which may beof quartz, contains an anode 23 which may be a tungsten or tantalum rod,and has an end opening 24 of the size and shape desired for the lightsource. The tube 22 may be of opaque quartz or have its surface etchedor covered with an opaque substance. A cathode 25 of metal, such astantalum, which may be a cylinder of sheet metal, surrounds the tube 22and may be supported from a lead 26 sealed into the wall of envelope 2I. The method of construction andmode of operation of this embodiment ofmy invention are similar to those already described in connection withFigs. 1 and 2.

While, in accordance with the patent statutes, I have described indetail two particular embodiments of my invention, it will be evidentthat the principles thereof may be embodied in numerous other structureswhich will be readily devised by those skilled in the art. Accordingly,I desire that the following claims be limited only in accordance withtheir express terms and in view of the prior art.

I claim as my invention:

1'. An electrical-discharge device comprising a vacuum-tight container,a cathode having an opening therein, an anode adjacent to said cathodeand having an opening therein in alignment with the opening in saidcathode, and an insulating member positioned between said cathode andsaid anode and intersecting all straight line discharge paths betweensaid anode and cathode, said member having an opening in alignment withsaid first-named openings.

2. In a device of the class described, a bulb including a substantiallyflat optical window, a pair of spaced electrodes within the bulb, and amember interposed between one of said electrodes and said window andformed with a narrow elongated slit through which lightmay pass.

3. A source of light for producing a photographic record of light wavevariations comprising a bulb having a substantially flat optical window,a cathode within the bulb, an anode within the bulb, an ionizable gaswithin the bulb, and a member interposed between the cathode and saidwindow and formed with a slit permitting the passage of light rays.

4. A source of light for producing a photographic record of light wavevariations comprising a bulb having a substantially flat optical window,a cathode within the bulb, an anode within the bulb, an ionizable gaswithin the bulb, and a member interposed between the cathode and saidwindow and formed with a slit aligned with the cathode.

5. A source of light for producing a photographic record of light wavevariations comprising a bulb, a cathode within the bulb, an anode withinthe bulb, a metallic disc between the oathode and the wall of the bulb,and said disc formed with a narrow elongated slit positioned in front ofthe cathode.

6. A source of light for producing a photographic record of light wavevariations comprising a bulb including a substantially flat opticalwindow, an anode within the bulb, a cathode within the bulb, anionizable gas within the bulb at such a pressure that at operatingvoltage'a concentrated glow is produced about the cathode, an

opaque member positioned between the cathode and said window and formedwith a narrow elonated slit.

7. A source of light for producing a photographic record of light wavevariations comprising a bulb including a substantially flat opticalwindow, an anode within the bulb, a cathode within the bulb, anionizable gas within the bulb at such a pressure that at operatingvoltage a concentrated glow is produced about the cathode, an opaquemember positioned between the oathode and said window and formed with anarrow elongated slit extending substantially parallel with the cathode.

8. A source of light for producing a photographic record of light wavevariations comprising a bulb having a substantially flat transparentoptical end, means for producing a glow within the bulb, and a memberwithin the bulb provided with a narrow elongated slit.

9. An electrical-discharge device comprising a first electrode, walls ofinsulating material surrounding said electrode, said walls having anaperture at one point therein and a second electrode comprising a hollowmember outside said walls and having an opening registering with saidaperture, said walls of insulating material intersecting all straightline discharge paths between said two electrodes.

10. An electrical-discharge device comprising a first electrode, wallsof insulating material surrounding said electrode, said walls having anaperture at one point therein and a second electrode comprising a hollowmember closely surrounding said aperture and covering an extended areathereabout and intersecting all straight line discharge paths betweensaid electrodes.

11. An electrical discharge device comprising a container having anoptical window, two electrodes in said container, a gaseous mediumproviding a luminous discharge path between said electrodes, aninsulating wall intersecting all straight line discharge paths betweensaid electrodes, said insulating wall having an opening aligned withsaid optical window.

12. An' electrical discharge device comprising a container having anoptical window, two electrodes in said container, at least one of saidelectrodes having an aperture therein, a gaseous medium providing aluminous discharge path between said electrodes, an insulating wallintersecting all straight line discharge paths between said electrodes,said insulating wall having an opening aligned with said optical window;

DEWEY D. KNOWLES.

